package cn.zust.ly.ExExample.Ex01;

import java.util.Scanner;

/**
 * Created by liy on 2016/11/14.
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while(true){
            long b = sc.nextLong();

            System.out.println((1+b)*b/2);

//            BigInteger a = sc.nextBigInteger();
//            BigInteger sum = a;
//            while (a.longValue() > 0) {
//                a = a.add(new BigInteger("-1"));
//                sum = sum.add(a);
//            }
//            System.out.println(sum);
        }

    }
}
